Wire heated tube with temperature control system for humidifier for respiratory apparatus

ABSTRACT

A PAP system for delivering breathable gas to a patient includes a flow generator to generate a supply of breathable gas to be delivered to the patient; a humidifier including a heating plate to vaporize water and deliver water vapor to humidify the supply of breathable gas; a heated tube configured to heat and deliver the humidified supply of breathable gas to the patient; a power supply configured to supply power to the heating plate and the heated tube; and a controller configured to control the power supply to prevent overheating of the heating plate and the heated tube.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/169,714, filed Jan. 31, 2014, now allowed, which claims the benefitof Australian Provisional Application No. 2013900328, filed Feb. 1,2013, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present technology relates to humidification and heater arrangementsused to control the humidity of breathable gases used in all forms ofrespiratory apparatus ventilation systems including invasive andnon-invasive ventilation, Continuous Positive Airway Pressure (CPAP),Bi-Level therapy and treatment for sleep disordered breathing (SDB)conditions such as Obstructive Sleep Apnea (OSA), and for various otherrespiratory disorders and diseases.

2. Description of Related Art

Respiratory apparatus commonly have the ability to alter the humidity ofthe breathable gas in order to reduce drying of the patient's airway andconsequent patient discomfort and associated complications. The use of ahumidifier placed between the flow generator and the patient mask,produces humidified gas that minimizes drying of the nasal mucosa andincreases patient airway comfort. In addition in cooler climates, warmair applied generally to the face area in and about the mask, as mayoccur inadvertently by a leak, is more comfortable than cold air.

Many humidifier types are available, although the most convenient formis one that is either integrated with or configured to be coupled to therelevant respiratory apparatus. While passive humidifiers can providesome relief, generally a heated humidifier is required to providesufficient humidity and temperature to the air so that patient will becomfortable. Humidifiers typically comprise a water tub having acapacity of several hundred milliliters, a heating element for heatingthe water in the tub, a control to enable the level of humidification tobe varied, a gas inlet to receive gas from the flow generator, and a gasoutlet adapted to be connected to a tube that delivers the humidifiedpressurized gas to the patient's mask.

Typically, the heating element is incorporated in a heater plate whichsits under, and is in thermal contact with, the water tub.

The humidified air may cool on its path along the conduit from thehumidifier to the patient, leading to the phenomenon of “rain-out”, orcondensation, forming on the inside of the conduit. To counter this, itis known to additionally heat the gas being supplied to the patient bymeans of a heated wire circuit inserted into the tube that supplies thehumidified gas from the humidifier to the patient's mask. Such a systemis illustrated in Mosby's Respiratory Care Equipment (7th edition) atpage 97.

Alternatively the heating wire circuit may be located in the wall of thewire heated tube. Such a system is described in U.S. Pat. No. 6,918,389which describes a number of humidifier arrangements for supplying lowrelative humidity, high temperature humidified gas to the patient. Someof these arrangements include pre- or post-heating of the gas to reducethe relative humidity.

None of these prior art devices provide accurate temperaturemeasurements during continuous use of a heated tube or conduit.

SUMMARY OF THE INVENTION

Examples of the present invention aim to provide an alternative PAPsystem which overcomes or ameliorates the disadvantages of the priorart, or at least provides a useful choice.

According to one aspect, a heated tube or conduit is provided to arespiratory apparatus to deliver the warm and/or humidified air andminimise condensation in the tube or conduit.

According to another aspect, a heated tube or conduit is provided thatallows for measurement and/or control of the delivered air temperature.

According to yet another aspect, a temperature measurement and/orcontrol system is provided that allows monitoring of the temperature inthe heated tube or conduit during at least a portion of the period whenthe heating circuit of the heated tube is on. Preferably, a temperaturemeasurement and/or control system allows measurement of the temperatureduring both periods when the heating circuit of the heated tube is onand when the heating circuit is off.

According to yet another aspect, a temperature measurement and/orcontrol system is provided that includes a bias generator that allowsthe temperature of the heated tube or conduit to be monitored during atleast of portion of the time while the heating circuit is on or active.

According to yet another aspect, a sensing circuit for a heated conduitfor use in a respiratory apparatus is provided, the sensing circuitcomprising a sensing wire coupled to a heating circuit for the heatedconduit, a temperature sensor coupled to the sensing wire and configuredto measure the temperature of the heated conduit, a sensing resistorcoupled to the sensing wire and configured to provide an output toindicate the temperature measured by the temperature sensor and a biasgenerator circuit configured to provide a reference voltage to thesensing resistor to allow determination of the output as a function of avoltage drop across the sensing resistor during both heating on andheating off cycles of the heating circuit, wherein the bias generatorincludes a track and hold circuit configured to measure a voltage of thesensing wire and provide the measured voltage to the bias generatorcircuit, wherein the bias generator circuit is configured to adjust thereference voltage as a function of the measured voltage.

According to an even further aspect, a heating plate of the humidifierand the heated tube may be controlled to prevent overheating of theheating plate and the heated tube that may occur due to differencesbetween actual temperatures and temperatures provided by temperaturesensors.

In one sample embodiment of the technology, a control system for aheated conduit for use in a respiratory apparatus comprises a powersupply to provide power to the heated conduit; an over temperaturecontrol circuit to prevent the overheating of the heated conduit; aheating control circuit configured to control heating to obtain adesired temperature; a sensing circuit including a sensing resistorconfigured to indicate the temperature of a sensor positioned in theheated conduit; and a bias generator circuit configured to provide afirst source voltage to the sensing circuit so that the temperature ofthe heated conduit is continuously monitored.

According to another sample embodiment, a conduit for use in arespiratory apparatus for delivering breathable gas to a patientcomprises a tube; a helical rib on an outer surface of the tube; a tubecircuit comprising at least three wires supported by the helical rib incontact with the outer surface of the tube and a temperature sensorconnected to at least one of the three wires to provide a signal to apower supply and controller of the respiratory apparatus; and a firstcuff connected to a first end of the tube and a second cuff connected toa second end of the tube, the first cuff being configured to beconnected to a patient interface of the respiratory apparatus and thesecond cuff being configured to be connected to a flow generator orhumidifier of the respiratory apparatus.

In another sample embodiment, a control system for a heated conduit foruse in a respiratory apparatus is provided, the control systemcomprising a power supply to provide power to the heated conduit, aheating control circuit configured to control heating to obtain apredetermined temperature, a sensing circuit configured to indicate thetemperature of a sensor positioned in the heated conduit and a biasgenerator circuit configured to provide a current to the sensor from acurrent source such that a voltage drop through the sensor may berecorded by the sensing circuit so that the temperature of the heatedconduit is continuously monitored independent of whether the heatingcontrol circuit is on or off.

In another sample aspect, a control system for a heated conduit for usein a respiratory apparatus is provided, the control system comprising apower supply to provide power to the heated conduit, a heating controlcircuit configured to control heating to obtain a predeterminedtemperature, a sensing circuit including a sensing resistor configuredto provide an output to indicate the temperature of a sensor positionedin the heated conduit and a bias generator circuit configured to providea reference voltage to the sensing resistor to allow determination ofthe temperature of the heated conduit as a function of a voltage dropacross the sensing resistor during both heating on and heating offcycles, wherein a direction of the voltage drop across the sensingresistor changes when the heating circuit is on compared to when theheating circuit is off.

In another sample embodiment, a respiratory apparatus for deliveringbreathable gas to a patient comprises a flow generator to generate asupply of breathable gas to be delivered to the patient; a humidifier tovaporize water and to deliver water vapor to humidify the gas; a firstgas flow path leading from the flow generator to the humidifier; asecond gas flow path leading from the humidifier to the patientinterface, at least the second gas flow path comprises a conduitaccording to at least the preceding paragraph; and a power supply andcontroller configured to supply and control power to the conduit throughthe cuff.

In yet another sample embodiment, a PAP system for delivering breathablegas to a patient comprises a flow generator to generate a supply ofbreathable gas to be delivered to the patient; a humidifier including aheating plate to vaporize water and deliver water vapor to humidify thesupply of breathable gas; a heated tube configured to heat and deliverthe humidified supply of breathable gas to the patient; a power supplyconfigured to supply power to the heating plate and the heated tube; anda controller configured to control the power supply to preventoverheating of the heating plate and the heated tube.

In a further sample embodiment, a patient interface for use in arespiratory system comprises an assembly configured to sealingly engagethe face of a patient; at least one circuit configured to receive asupply of power and send and receive data, a portion of the at least onecircuit being removably attachable to a link from which the data andpower is supplied; at least one sensor in communication with the atleast one circuit; and at least one controller in communication with theat least one circuit.

In a still further sample embodiment, a method of controlling a heatedconduit connected to a respiratory apparatus comprises supplying powerto the heated conduit; continuously monitoring a temperature of a sensorpositioned in the heated conduit; and controlling the power supply tothe heated conduit to obtain a desired temperature.

In still another sample embodiment, a method for delivering breathablegas to a patient comprises generating a supply of breathable gas;vaporizing water using a heating plate; delivering water vapor tohumidify the supply of breathable gas; heating and delivering thehumidified supply of breathable gas to the patient using a heated tube;and controlling a power supply to the heating plate and heated tube toprevent overheating of the heating plate and the heated tube.

BRIEF DESCRIPTION OF THE DRAWINGS

Sample embodiments will be described with reference to the accompanyingdrawings, in which:

FIG. 1 schematically depicts a PAP system according to a sampleembodiment;

FIG. 2 schematically depicts a PAP system according to another sampleembodiment;

FIG. 3 schematically depicts a PAP system according to another sampleembodiment;

FIG. 4 schematically depicts of a PAP system including a flow generatorand humidifier according to a sample embodiment;

FIGS. 5-7 schematically depict the humidifier of FIG. 4;

FIG. 8 schematically depicts a heated tube according to a sampleembodiment;

FIGS. 9-13 schematically depict a connector, or cuff, of the tube ofFIG. 8 at an end of the tube configured to be connected to a humidifier;

FIG. 14 schematically depicts the end of the tube of FIGS. 9-13connected to the humidifier of FIGS. 5-7;

FIG. 15 schematically depicts an end of the tube of FIG. 8 connected toa patient interface;

FIGS. 16 and 17 schematically depict a connector, or cuff, of the end ofthe tube of FIG. 8 configured to be connected to a patient interface;

FIG. 18 schematically depicts a wiring configuration for the heated tubeof FIG. 8;

FIG. 19 schematically depicts a sample embodiment of an algorithm forcontrolling the heated tube;

FIG. 20 schematically depicts a circuit according to another sampleembodiment that senses a temperature at the patient interface andprovides active over temperature protection;

FIG. 20A schematically depict a circuit similar to that shown in FIG. 20showing an alternative bias generator circuit arrangement;

FIG. 20B schematically depict a circuit similar to that shown in FIG. 20showing an alternative bias generator circuit arrangement including atrack and hold circuit;

FIG. 20C schematically depict a circuit similar to that shown in FIG. 20showing an alternative bias generator circuit arrangement including atrack and hold circuit;

FIG. 20D schematically depicts a circuit showing an alternative biasgenerator circuit arrangement having a current source;

FIG. 20E schematically depict a circuit similar to that shown in FIG. 20showing an alternative bias generator circuit arrangement;

FIG. 21 schematically depicts a circuit according to still anothersample embodiment that senses a temperature at the patient interface,detects a tube type, and provides active over temperature protection;

FIG. 22 schematically depicts a circuit according to yet another sampleembodiment that senses a temperature at the patient interface, detects atube type, provides active over temperature protection, and detects aconnection fault;

FIG. 23 schematically depicts a relationship between a resistance of atemperature sensor and temperature according to sample embodiments;

FIG. 24 schematically depicts an algorithm for controlling the heatingplate of the humidifier according to a sample embodiment;

FIG. 25 schematically depicts an algorithm for controlling the heatedtubing according to yet another sample embodiment;

FIG. 26 schematically depicts a PAP system with a Powered PatientInterface according to a further sample embodiment;

FIG. 27 schematically depicts a circuit according to yet another sampleembodiment that facilitates communication of data and power out of thecircuit;

FIG. 28 schematically depicts a circuit in a patient interface deviceaccording to a further sample embodiment;

FIG. 29 schematically depicts a humidifier heating plate according to asample embodiment;

FIGS. 30 and 31 schematically depict a humidifier heating plateaccording to another sample embodiment;

FIG. 32 schematically depicts a humidifier heating plate according toyet another sample embodiment; and

FIG. 33 schematically depicts a humidifier heating plate according to astill further sample embodiment.

FIG. 34 schematically illustrates an example switching arrangement forthe transistor switches shown in FIG. 20B showing a sampling time priorto the heating on cycle.

FIG. 35 schematically illustrates an example switching arrangement forthe transistor switches shown in FIG. 20C showing a sampling time priorto both a heating on and a heating off cycle.

FIG. 36 schematically illustrates a circuit that senses a temperature atthe patient interface regardless of whether the air delivery tube isbeing heated.

FIG. 37 graphically illustrates a rate of discharging/charging of acapacitor in the circuit of FIG. 36.

DETAILED DESCRIPTION

PAP System

As schematically shown in FIG. 1, a Positive Airway Pressure (PAP)system, for example a Continuous Positive Airway Pressure (CPAP) system,generally includes a PAP device (or PAP system or respiratory apparatus)10, an air delivery conduit 20 (also referred to as a tube or tubing),and a patient interface 50. In use, the PAP device 10 generates a supplyof pressurized air that is delivered to the patient via an air deliveryconduit 20 that includes one end coupled to the outlet of the PAP device10 and an opposite end coupled to the inlet of the patient interface 50.The patient interface comfortably engages the patient's face andprovides a seal. The patient interface or mask may have any suitableconfiguration as is known in the art, e.g., full-face mask, nasal mask,oro-nasal mask, mouth mask, nasal prongs, etc. Also, headgear may beutilized to comfortably support the patient interface in a desiredposition on the patient's face.

In embodiments, a humidifier may be incorporated or integrated into thePAP device or otherwise provided downstream of the PAP device. In suchembodiments, the air delivery conduit 20 may be provided between thepatient interface 50 and the outlet of the humidifier 15 asschematically shown in FIG. 2.

It should be appreciated that the air delivery conduit may be providedalong the air delivery path in other suitable manners. For example, asschematically shown in FIG. 3, the humidifier 15 may be a separatecomponent from the PAP device 10 so that an air delivery conduit 20(1)is placed between the PAP device 10 and the humidifier 15 and anotherair delivery conduit 20(2) is placed between the humidifier 15 and thepatient interface 50.

Generally, a heated humidifier is used to provide sufficient humidityand temperature to the air so that the patient will be comfortable. Insuch embodiment, the air delivery conduit may be heated to heat the gasand prevent “rain-out” or condensation forming on the inside of theconduit as the gas is supplied to the patient. In this arrangement, theair delivery conduit may include one or more wires or sensors associatedwith heating.

As described below, each end of the air delivery conduit includes a cuffstructured to attach the tube to the patient interface, PAP device,and/or humidifier. The cuffs differ for non-heated tubes and heatedtubes, e.g., cuffs for heated tubes accommodate sensors orelectronics/wiring associated with heating.

While the cuff is described as being implemented into a CPAP system ofthe type described above, it may be implemented into other tubingarrangements for conveying gas or liquid. That is, the CPAP system ismerely exemplary, and aspects of the present invention may beincorporated into other suitable arrangements.

Referring to FIGS. 4-7, a PAP system 10 according to a sample embodimentcomprises a flow generator, or blower, 12 and a humidifier 15. The flowgenerator 12 is configured to generate a flow of breathable gas having apressure of, for example, about 2-30 cm H₂O. The flow generatorcomprises a power button 2 to turn the PAP system on and off. A display4 is provided to display interactive menus and information regarding theoperation of the PAP system to the user or operator. The user oroperator may select menus and/or information through inputs 6, which maybe, for example, buttons or keys. A push button dial 8 may also allowthe user or operator to select information and/or menus. The inputs 6and the push button dial 8 may be used together to select informationand/or menus. For example, one or both of the inputs 6 may be pressedand the dial 8 may be rotated to display desired information or menu onthe display 4 and the dial 8 may then be pressed to select particularinformation to be displayed or a particular mode of operation of the PAPsystem.

The humidifier 15 comprises a humidifier chamber 16 and a lid 18 whichis pivotable between an open and a closed position. A water chamber, ortub, 14 is provided in the humidifier chamber 16 and is covered by thelid 18 when the lid 18 is in the closed position. A seal 19 is providedto the lid 18. The lid 18 includes a window 30 to allow visualinspection of the contents of the humidifier tub 14. The seal 19includes an aperture 31 that corresponds to the position of the window30 of the lid 18. In the closed position of the lid 18, the seal 19contacts the tub 14 to ensure good thermal contact between a bottom ofthe tub 14 and a heating plate (not shown) provided in the bottom of thehumidifier chamber 16 as disclosed, for example, in WO 2010/031126 A1.The tub 14 comprises a base, or bottom, that conducts heat from theheating plate to a supply of water provided in the tub 14. Such tubs aredisclosed in WO 2010/031126 A1.

As shown in FIGS. 4 and 5, the humidifier 15 is connectable to the flowgenerator 12 by connectors, or latches, 24. The latches 24 may be, forexample, spring biased latches that engage corresponding recesses (notshown) in the flow generator 12. An electrical connector 26 is providedto electrically connect the flow generator 12 to the humidifier tub 14.Electrical power may be provided from the flow generator 12 to thehumidifier tub 14, although it should be appreciated that the humidifiermay be provided with its own power source. Control signals may also beprovided from the flow generator 12 to the humidifier tub 14 through theelectrical connector 26.

As shown in FIG. 4, the tub 14 comprises a tub lid (or top) 86 that isconfigured to direct a flow of breathable gas generated by the flowgenerator 12 along a channel 90 in the tub lid 86 and through an outlet92 of the channel 90 into the tub 14. The humidifier chamber 16 includesan air inlet 22 configured to receive the flow of breathable gasgenerated by the flow generator 12 when the humidifier 15 is connectedto the flow generator 12 by the latches 24. The inlet 22 directs theflow into the channel 90 in the tub lid 86 of the humidifier tub 14. Theflow is directed by the channel 90 to the outlet 92 into the humidifiertub 14. The tub 14 includes an outlet 88 for the humidified flow ofbreathable gas. A tube connector 70 (FIG. 7) is provided at a rearportion of the humidifier 15 in communication with the outlet 88. Itshould be appreciated that the tube connector 70 may be provided on aside, or the front, of the humidifier 15. The tube connector 70 isconfigured for connection to a hose, tube, or conduit to a tube that isconfigured to deliver the humidified flow to patient interface, e.g. amask, as described in more detail herein.

It should be appreciated that the humidifier 15 may include its owncontrol system, or controller, for example, a microprocessor provided ona printed circuit board (PCB). The PCB may be located in the wall of thehumidifier chamber 16 and may include a light, e.g. an LED, toilluminate the contents of the tub 14 to permit visual inspection of thewater level. It should also be appreciated that the flow generator 12comprises a control system, or controller, that communicates with thecontroller of the humidifier 15 when the flow generator 12 and thehumidifier 15 are electrically connected. It should be furtherappreciated that the flow generator and/or the humidifier may include aplurality of sensors, including for example, an ambient humidity sensorthat may be configured to detect, for example, absolute ambient humidityand which may include an absolute humidity sensor or a temperaturesensor to detect an ambient temperature and a relative humidity sensorto detect an relative humidity from which the ambient absolute humiditymay be calculated. The plurality of sensors may also include, forexample, an ambient pressure sensor to detect an ambient pressure, aflow sensor to detect a flow of breathable gas generated by the flowgenerator, and/or a temperature sensor to detect a temperature of asupply of water contained in the tub 14 of the humidifier 15 or thetemperature of the heating plate of the humidifier 15. Such anarrangement is shown, for example, in U.S. Patent ApplicationPublication 2009/0223514 A1. The PAP system 10 may be operated accordingto various control algorithms stored in the controller(s) of the flowgenerator 12 and/or the humidifier 15. Such control algorithms aredisclosed in, for example, U.S. Patent Application Publication2009/02223514 A1.

The humidifier 15 comprises the humidifier chamber 16 and the lid 18which is pivotally connected to the humidifier chamber 16. As shown inFIG. 6, the lid 18 comprises a hinge portion 17 that is hinged to hingeportions 47 provided on the humidifier chamber 16. An opening member 28is provided for releasing the lid 18 to allow the lid to be pivoted tothe open position shown in FIGS. 4 and 6 as described in WO 2010/031126A1.

Referring to FIG. 7, the humidifier comprises the tube connector 70 anda tube electrical connector 75. The tube connector 70 and the tubeelectrical connector 75 provide the ability to connect both a standardtube and a heated tube. As shown in FIG. 7, the tube electricalconnector 75 comprises a plurality of contacts 78. The tube electricalconnector 75 and the contacts 78 are provided separately from the tubeconnector 70. A heated tube having corresponding electrical connections,e.g. terminals, may be provided in a rotational snap fit with the tubeelectrical connector 75 as described in more detail below. This type ofconnection provides ease of connection and reduces the tolerance stackof the PAP system 10. A cover 132 may be connected to the back wall ofthe humidifier 15 to cover the tube connector 75 and the contacts 78when a non-heated tube is connected to the tube connector 70. The cover132 may be formed of a pliable rubber or other suitable flexiblematerial. Alternatively the cover 132 may be a separate component, notattached to the humidifier that may be inserted over the tube electricalconnector 75.

Heated Tube/Conduit

FIG. 8 illustrates an embodiment of a heated air delivery conduit ortube. The heated tube 320 comprises a flexible tube 325, a firstconnector, or cuff, 330(1) provided to one end of the tube 325 andconfigured and arranged to engage the tube connector 70 and the tubeelectrical connector of the humidifier 15, and a second cuff 330(2)provided to the opposite end of the tube 325 and configured and arrangedto engage the inlet (e.g. a swivel elbow) of a patient interface 50, asshown in FIG. 15. The heated tube 320 may be, for example, as disclosedin U.S. Patent Application Publication 2010/0116272 A1.

The tube 320 is structured to conduct heat along at least a portion ofits length. For example, spiral ribbing 328 of the tube 325 may bestructured to support three wires 504, 506, 508 (FIGS. 15 and 18). Inaddition, the heated tube 320 may be structured to support one or moresensing apparatus, e.g. a flow sensor and/or a temperature sensor, etc.Further details of such tubing are disclosed in U.S. Patent ApplicationPublication 2008/0105257 A1.

In the illustrated embodiment, the cuffs 330(1), 330(2) are differentfrom one another as described below. However, each cuff providesstructure for attaching, sealing, and retaining the cuff to a respectiveconnector, e.g., 22 mm ISO-taper connector.

The opening of the cuff 330(1) includes a radial lip seal or sealing lip331 along the interior surface thereof. As shown in FIG. 13, the radialsealing lip 331, in its relaxed, undeformed shape, provides an internaldiameter dl that is smaller than the external diameter of the tubeconnector 70. For example, the internal diameter may be less than about22 mm (e.g., about 19-21 mm or less) for use with a standard 22 mmconnector. In use, as best shown in FIG. 14, the sealing lip 331 isstructured to resiliently deform upon engagement with the tube connector70 so as to provide a gas tight seal against the exterior surface of thetube connector 70. For example, the sealing lip 331 provides a flexibleprotrusion structured to resiliently deflect from a first position (FIG.13) and into a second position (FIG. 14) within a cut-out 335.

As illustrated, the sealing lip 331 tapers outwardly towards the cuffopening to provide a sufficient lead in for aligning and engaging thecuff 330(1) with the tube connector 70.

The interior surface 333 axially inwardly from the sealing lip 331provides an internal diameter that is substantially the same as theexternal diameter of the tube connector 70, e.g., about 22 mm for usewith a standard 22 mm connector. A stop surface or flanged faced 336within the cuff 330(1) provides a stop to prevent the tube connector 70from inserting further into the cuff 330(1).

FIGS. 9-14 illustrate the cuff 330(1) structured for attachment to thehumidifier 15. The cuff 330(1) includes an electrical connector 60 thatis configured to provide an electrical connection with the humidifier 15for operating the heating wires 504, 506, 508 (FIG. 15) provided to thetube 320. The electrical connector 60 includes terminals 62 that areconfigured to receive the contacts 78 of the tube electrical connector75 of the humidifier 15 when the cuff 330(1) is connected to the tubeconnector 70 of the humidifier 15. The electrical connector 60 providesa retention function for the cuff 330(1). Retention is via arotate-and-lock system to align the terminals 62 of the electricalconnector 60 with the contacts 78 of the tube electrical connector 75 ofthe humidifier 15. The electrical connector 60 provides a heel 64structured to be rotated into engagement with the tube electricalconnector 75 such that the heel 64 locks into a cam or recess providedto the tube electrical connector 75 of the humidifier 15. When engaged,the heel 64 axially locks the cuff 330(1) into place. To release, thecuff 330(1) is rotated out of engagement with the tube electricalconnector 75 to disengage the heel 64. As shown in FIG. 13, a seal 66extends from the front, back, side, and bottom of the electricalconnector 60 and seals against the tube electrical connector 75 of thehumidifier 15 to prevent water spillage onto the electrical contacts 78and the terminals 62.

The cuff 330(1) may comprise finger grips 340 along opposing sidesthereof and along an edge of the electrical connector 60. The cuff330(1) may also comprise an identifying strip 341 (e.g., orange strip)to identify the tube as a heated tube. A similar identifying strip maybe provided to the user interface of the PAP system 10 and configured toilluminate or otherwise signal when the heated tube is operative, e.g.,heating up, heated, etc. In addition, indicia and/or images 343 may beprovided to the cuff 330(1) to indicate directions for locking andunlocking the cuff 330(1) with respect to the humidifier 15.

Referring to FIGS. 15-18, the cuff 330(2) at the opposite end of theheated tube 320 is configured for attachment to the patient interface(e.g. mask) 50. The cuff 330(2) comprises a sensor 45 located (e.g.,molded into) within the rear portion of the cuff. The cuff 330(2)includes a curved entry surface 35, a sealing and retention bead 37, anda stop surface 39 to aid connection of the heated tube 320 to thepatient interface 50.

The sensor 45 is provided to a fixture 46 within the cuff. In theillustrated embodiment, the fixture 46 is wing-shaped (e.g. air-foilshaped) to optimize convective heat transfer over a range of flow rates,while minimizing noise or pressure drop. However, the fixture 46 mayhave other suitable shapes and/or textures. The cuff 330(2) may beformed by, for example, overmolding on a pre-block 49, or any methoddisclosed, for example, in U.S. Patent Application Publication2008/0105257 A1, which is incorporated herein by reference in itsentirety. The sensor 45 may be connected to the wires 504, 506, 508 inthe heated tube 320 by a lead frame 48. The temperature sensed by thesensor 45 may be provided as a signal from the middle wire 504 throughthe lead frame 48 to a controller located in the humidifier 15 and/orthe PAP system 10.

As shown in FIG. 18, the sensor 45 may take the form of a thermistor 410formed of a Negative Temperature Coefficient (NTC) material. Asdescribed in more detail below, the middle wire 504 of the three wires504, 506, 508 of the tube circuit 402 may be connected to the thermistor410 and provide the temperature sensing signal to the controller. Twowires 506, 508 may be joined together at the lead frame 48 to completethe heating circuit. The third wire 504 provides a connection to the NTCthermistor which may be attached to the mid-point 507 of the heatingcircuit. The two heating wires 506, 508 may be low ohmic value resistorsto apply heat to the tube wall and therefore to the air being deliveredto the patient. The signal wire 504 may be fitted with the thermistor410 located at the patient interface end of the heated tube 320. Thesignal wire 504 monitors the temperature of the air at the patientinterface end of the heated tube and detects any imbalance between thebridge formed by the two heater wires 506, 508. The imbalance may beused to detect a fault condition, for example high impedance or an opencircuit and low impedance or a short circuit.

Heated Tube Control

The heated tube 320 may be used to deliver the comfort of warm,humidified air and minimise condensation in the tubing. Referring toFIG. 19, an algorithm for controlling a heated tube is shown. Thealgorithm starts at S300 and determines the temperature sensed by atemperature sensor in the heated tube (e.g. thermistor 410) in S302. Thealgorithm proceeds to S306 and determines if the sensed temperature isoutside a predetermined range. If the temperature of the heated tube isnot outside the predetermined range (S306: No), the algorithm ends inS316. Conversely, if the temperature is outside the predetermined range(S306: Yes) the algorithm proceeds to S310 and it is determined if thetemperature is above the predetermined range. If the temperature isbelow the predetermined range (S310: No), the algorithm proceeds to S312and power is supplied to the heated tube. If the sensed temperature isabove the predetermined range (S310: Yes), the algorithm proceeds toS314 shuts off power to the heated tube. After the completion of S312 orS314 the algorithm returns to the beginning in S300, thus providingtemperature control for the heated tube.

The control of the heated tube may involve several considerations. Oneconsideration is to measure and control the delivered air temperature inthe heated tube system with a low cost tube assembly. Anotherconsideration is, for safety, a failsafe mechanism may be provided toensure the delivered air temperature does not exceed a safe temperaturelimit. Still another consideration is that it may be desirable toautomatically identify whether the heated tube that is attached to thehumidifier and/or flow generator has a 15 mm or 19 mm internal diameter.The pneumatic performance of the system may require compensation in theblower drive circuitry depending on which internal diameter tube ispresent.

According to another consideration, for safety, it is desirable todetect failures in the heated tube, such as high resistance hot spots inthe wires or short circuits between the wires part way down the lengthof the tubing. A further consideration is that the heated tube may makeboth electrical and pneumatic connection to the humidifier in a simpleattachment process.

Current heated tube systems do not directly regulate the temperature ofthe air delivered. They are implemented as open loop control of tubeheating using a fixed power level. Although it may be possible toimplement a thermal cut-out switch within the structure of the tube,these devices are relatively large and require additional circuitconnections and mechanical mounting that add significant complexity tothe tube.

Heated Tube Control—Temperature Sensing with Active Over TemperatureProtection

Referring to FIG. 20, a circuit configuration 400 according to a sampleembodiment allows control of the tube air temperature using a sensor atthe output (mask) end of the tube. The heated tube circuit 402 comprisesthe three wires 504,506, 508 and the temperature sensor, e.g. the NTCthermistor 410 that are located within the heated tube. The wires 404,406, 408 are used in the sensing and control circuit to create a lowercost heating and sensing system with only three wires and are connectedto the three wires 504, 506, 508 respectively. As shown in FIG. 18, thethree wires 504, 506, 508 of the heated tube circuit 402 are connectedto different components of the sensing and control circuit to provide asensing wire 404, 504, a power supply wire 406 and a ground wire 408.The sensing and control circuits may be provided in a power supply andcontroller of the humidifier and/or flow generator. Such a power supplyand controller is disclosed in, for example, U.S. Patent ApplicationPublication 2008/0105257 A1. The complete sensing wire is formed ofwires 404 and 504.

Referring again to FIG. 20, the circuit configuration 400 comprises apower supply 440, such as a 24V supply voltage, an over-temperaturecontrol circuit and a heating control circuit. The over-temperaturecontrol circuit comprises a first transistor switch 420 that is turnedon when the temperature of the heated tube is below a predeterminedtemperature and turned off when the temperature is at or above thepredetermined temperature. The predetermined temperature is set at atemperature to meet appropriate safety requirements of the heated tube,such as between 30° C. and 45° C., preferably 38° C. to 43° C.Comparator 436 controls the switching of the transistor switch 420. Areference voltage representing the predetermined temperature is comparedto the voltage determined from an amplifier 430 from the sensing circuitto ensure the heated tube is not above or equal to the predeterminedtemperature.

Within the over-temperature control circuit is the heating controlcircuit which is designed to control the heating of the heated tube toobtain a desired temperature. The desired temperature may be set by theuser or determined by the system. The heating control circuit switchesthe power supply 440 through the heated tube circuit 402 to a groundreference 412. Thus, the temperature sensor 410 moves between groundhaving 0V and half the supply voltage, e.g. 12V. Heating is supplied tothe heated tube circuit 402 from power supply 440 through a secondtransistor switch 434. Transistor switch 434 is open and closed to turnheating on and off to the heated tube circuit 402 respectively. In oneembodiment this transistor switch 434 is switched on and off veryrapidly with changes in the duty cycle to control the heating of thetube. However, the switch 434 may be switched on to provide constantheating until a set temperature is reached and then turned off. Thetemperature of the heated tube is sensed by the temperature sensor 410and is transmitted through sense wire 404, 504 to sensing resistor 426and sensing circuit 428 comprising amplifier 430. A bias generatorcircuit 418 provides the bias source voltage Vcc for the sensing circuit428 so that the temperature of the heated tube is determined whether thetube is being heated or not. The bias generator circuit 418 generates areference voltage that is either the Vcc bias source voltage 414, shownas 5V in this embodiment although other voltages may be used, when thetube heating is off via switch 422 or provides half the voltage supplyplus the Vcc bias source voltage 416, i.e. 5V, when the tube heating ison via switch 424. Thus a constant voltage of Vcc bias source voltage isprovided across the sensing circuit 428 irrespective of the state of theheated tube. The switching of the bias switches 422, 424 is controlledby the transistor switch 434 of the heating control circuit, such thatwhen the transistor switch 434 is closed the tube heating ON switch 424is active and when the transistor switch 434 is open the tube heating ONswitch 424 is inactive. Thus, it is the voltage that is supplied to theheated tube circuit 402 that provides the bias switch.

The sensed temperature signal from the temperature sensor 410 isprovided to amplifier 430 that produces a voltage that represents theheated tube temperature. The temperature control block 432 controls theopening and closing of switch 434 to modulate the power delivered to theheated tube circuit to maintain the desired temperature.

The temperature sensor 410 is held at a different circuit potential whenthe heater is active and when it is inactive. However, the sensor 410should be continuously monitored to provide a failsafe against overtemperature. A bias circuit 418 may be provided for continuous sensing.A bias generator circuit may provide the source voltage for the sensingcircuit, a divider network comprising a resistor R1 and the NTCthermistor. This allows continuous temperature monitoring during bothheating and idle states of the sensing and control system, andfacilitates an active over temperature detection that is independent ofthe temperature control loop. Temperature sensing also remains activeduring the over temperature condition.

The circuit configuration may comprise a common ground referencedheating/sensing system with a supply voltage switching to the tubecircuit for heating control. An alternative approach is to utilise thesupply voltage as both the heating and sensing source voltage andcontrol heating by switching to 0V the tube circuit.

Alternative Bias Generator Arrangements

As described above the bias generator allows for a three wire heatedtube system to provide temperature sensing during the active heating orON cycle of the heating circuit as well as during the inactive or OFFcycle of the heating circuit. Temperature sensing remains active duringat least a portion, such as at least 50%, at least 75% or at least 90%or during 100% of both the active (ON) heating cycle and the inactive(OFF) heating cycle. Thus the temperature sensing circuit may providetemperature sensing throughout use of the heated tube irrespective ofthe heating status of the system.

An alternative bias generator arrangement 618 is shown in the heatingcircuit configuration 400A in FIG. 20A wherein the connection to theVoltage supply 440 for the bias generator is moved to a position afterthe transistor switch 434 that turns on and off the heating to theheated tube circuit 402. In this arrangement the Tube heating OFF switch422 and the Tube heating ON switch 424 are no longer required as thetransistor switch 434 will also function as the bias switch. To ensurethat the bias generator generates the same or substantially the samedifferential reference voltage to the sensing circuit 428 irrespectiveof whether the heating circuit is On or OFF, two additional resistors ofequal resistance 650 and 652 are provided to the bias generator circuitand a bias voltage circuit wire 654 is taken from a position betweenthese resistors to ensure the reference voltage provided to the sensingresistor 426 when the transistor switch 434 is closed is approximatelyhalf the voltage supply 440, being similar or substantially equal to thevoltage provided to the temperature sensor 410, plus the Vcc biasvoltage source 414. In addition, an amplifier 664 and resistors 666, 668and 670 may be provided to the bias generator circuit. The resistancevalues of the resistors 666, 668 and 670 may be chosen to sum and gainthe voltage at the bias voltage circuit wire 654 with the Vcc voltage atthe Vcc bias voltage source 414 in order to correctly bias the sensingresistor 426 for accurate measurement as the voltage at the power supplywire 406 changes from open circuit to the voltage when the switches 420and 434 are closed. The actual resistance values may be a function ofdesired bias voltage of the sensing resistor 426, the gain of theamplifier 430 and the characteristics of the temperature control block432 and the comparator 436.

The resistance provided to the temperature sensor 410 is approximated ashalf of the supply voltage due to sensing wire 404, 504 being located atthe wire junction 507 between the two heating wires 506, 508 and theresistance of the two heating wires 506, 508 are approximately equal.The Vcc bias voltage source 414 for the sensing circuit 428, for examplemay be 5 Volts, although other voltages may be used, is provided by thebias generator circuit and if the transistor switch 434 is closed isadded to the voltage provided from the voltage supply 440 via resistors650, 652 through wire 654. Thus the reference voltage provide to thesensing circuit 428 is half the voltage supply 440 plus the Vcc biasvoltage source 414 resulting in a net Vcc bias voltage source across thesensing resistor 426. In contrast if the transistor switch 434 is openthen no voltage is provided from the voltage source 440 to either of theheating circuit 402 and temperature sensor 410 or the bias generatorcircuit 618, therefore only the bias source voltage Vcc 414 is providedto the sensing resistor 426 for determining the output of the sensingcircuit 428 as a function of the voltage drop across the sensingresistor 426. Thus a constant net voltage differential of the Vcc biassource voltage is provided to the sensing resistor 426 irrespective ofwhether the heating circuit 402 is active (ON) or inactive (OFF) andallows sensing of the temperature of the heated tube during both the ONand OFF heating cycles of the heating circuit 402.

The bias generator arrangement as shown in FIG. 20B allows for improvedaccuracy in the temperature measurement, particularly when the heatingcircuit is ON or active. In this arrangement the system includes a trackand hold circuit 640 that measures the actual voltage at sensing wire404, 504 to compensate for variations in resistance through the circuitinstead of using an estimate of the voltage at sensing wire 404, 504during the active heating cycle. Instead of estimating that theresistance of the two heating wires 506, 508 are approximately equal andtherefore that the voltage at a location on the sensing wire 404, forexample at the wire junction 507 between the two heating wires 506, 508is half of the supply voltage, a measurement of the voltage may becarried out when the heating circuit is initially turned ON or activatedand/or made at regular intervals during the heating ON cycle or prior toturning off the heating circuit for use in the subsequent heating ONcycle or combinations thereof.

In a similar arrangement to the heating circuit configuration of FIG. 20the circuit configuration 400B comprises a power supply 440, such as a24V supply voltage, although other voltage supplies may be used, anover-temperature control circuit and a heating control circuit. Theover-temperature control circuit comprises a first transistor switch 420that is closed or ON when the temperature of the heated tube is below apredetermined temperature and opened or OFF when the temperature is ator above the predetermined temperature. The predetermined temperature isset at a temperature to meet appropriate safety requirements of theheated tube, such as between 30° C. and 45° C., preferably 38° C. to 43°C. Comparator 436 controls the switching of the transistor switch 420. Areference voltage representing the predetermined temperature is comparedto the voltage determined from an amplifier 430 from the sensing circuitto ensure the heated tube is not above or equal to the predeterminedtemperature.

Within the over-temperature control circuit is the heating controlcircuit which is designed to control the heating of the heated tube toobtain a desired temperature. The desired temperature may be set by theuser or determined by the system. The heating control circuit switchesthe power supply 440 through the heated tube circuit 402 to a groundreference 412. Thus, the temperature sensor 410 moves between groundhaving 0V and approximately half the supply voltage, e.g. 12V. Heatingis supplied to the heated tube circuit 402 from power supply 440 througha second transistor switch 434. Transistor switch 434 is opened andclosed to turn heating OFF and ON to the heated tube circuit 402respectively. In one embodiment this transistor switch 434 is switchedON and OFF very rapidly with changes in the duty cycle to control theheating of the tube. However, the switch 434 may be closed or ON toprovide constant heating until a set temperature is reached and thenopened or turned OFF. The temperature of the heated tube is sensed bythe temperature sensor 410 and is transmitted through sense wire 404,504 to sensing resistor 426 and sensing circuit 428 comprising amplifier430. A bias generator circuit 618 provides the bias source voltage Vcc614 to the sensing resistor 426 that provide an output for the sensingcircuit 428 so that the temperature of the heated tube may be determinedwhether the tube is being heated or not. The bias generator 618generates a reference voltage that is either the Vcc bias source voltage614 or a set measured voltage (Vset) plus the Vcc bias source voltage616 depending upon whether the heating circuit is OFF or ONrespectively. This ensures a constant voltage of the Vcc bias sourcevoltage is provided across the sensing circuit 428 irrespective of thestate of the heating circuit 402. The measured voltage (Vmea) isdetermined in a track and hold circuit 640 to provide an actual measureof the voltage in the heating circuit 402 at the wire junction 507between the two heating wires 506, 508 as described in more detailbelow.

The switching of the bias generator switches 622 and 624 is controlledby the transistor switch 434 of the heating control circuit, such thatwhen the transistor switch 434 is closed the transistor switch 624 isclosed and when the transistor switch 434 is open the transistor switch624 is open. A short delay may occur after the transistor switch 434closes and before the transistor switch 624 closes to allow the trackand hold circuit 640 to perform a measurement as described below. Thus,it is the voltage that is supplied to the heated tube circuit 402 thatprovides the bias switch. Alternatively a microprocessor may control theswitching of some or all of the various transistor switches 420, 434,622, 624, 626 and 628.

The track and hold circuit 640 comprises a transistor switch 628 that isused to turn the measurement ON and OFF and a capacitor 630 that storesthe measured voltage that is then provided through the heating circuitwhen the transistor switch 628 is open. The stored voltage is thenprovided as feedback to the Vset plus Vcc 616 and the new measured Vmeavalue replaces the previously set Vset value. Alternatively the newlymeasured voltage Vmea may be compared to the previously set measuredvoltage Vset to determine any difference between the values to provide avoltage error. The Vset value at 616 may then be adjusted to compensatefor the voltage error and reduce the voltage error level to zero.

The track and hold circuit 640 functions by temporarily closing thetransistor switch 628 for a sampling period when transistor switches 420and 434 are both closed and thus voltage is supplied to heating circuit402 such that the capacitor 630 will read or track the same voltage atthe wire junction 507 between the two heating wires 506, 508 of theheating circuit 402. The transistor switch 628 is closed for a samplingperiod of time during the heating cycle, i.e. when transistor switches420 and 434 are closed, to track the measured voltage Vmea. The samplingperiod is generally short for example 2-10 milliseconds such as 2.5, 5,6, 7, 8, 9 or 10 milliseconds, or for example a portion of a duty cycleof the heating circuit such as 1-25%, 2-20%, 5-15% or other portions ofa duty cycle of the heating circuit. For example, transistor switch 628may be closed for tracking the measured voltage Vmea at the commencementof the heating ON cycle or at any other time during the heating ONcycle. The bias generator transistor switches 622 and 624 are both openwhilst the voltage tracking is ON, i.e. whilst transistor switch 628 isclosed, to ensure an unbiased voltage is read by the capacitor 630.

Optionally, a further transistor switch 626 and capacitor 627 may beprovided after the sensing circuit 428 to temporarily prevent changes involtage being passed to the comparator 436 for the over temperaturecut-out or to the temperature control block 432 while the bias track andhold circuit is ON. The capacitor 627 would store the previouslyprovided voltage from the amplifier 430 and continue to provide thisvoltage to the comparator 436 and temperature control block 432. Thetransistor switch 626 would open when the transistor switch 628 closesand would then close when the transistor switch 628 opens, i.e. theswitches would operate in the inverse of each other.

FIG. 34 shows an example of how the transistor switches 434, 622, 624,626 and 628 may be operated to provide the heating ON and OFF cycles,the bias generator voltage and the track and hold cycle. It is notedthat transistor switch 420 is continuously closed or ON unless the overtemperature cut-out is activated. For the heating OFF cycle switches 622and 626 are closed so that the bias generator reference voltage is theVcc bias source voltage and the voltage is not being tracked by thetrack and hold circuit. To turn ON the heating cycle and to initiallysample (T) the voltage in the heating circuit the transistor switches622 and 626 are opened (i.e turned OFF) while transistor switches 434and 628 are closed (i.e. turned ON). This allows the track and holdcircuit 640 to measure the voltage at the wire junction 507 between thetwo heating wires 506, 508. After a short sampling period the transistorswitch 628 is opened (i.e. turned OFF) and the recorded measured voltageVmea is held by the capacitor 630. At the end of the sampling periodtransistor switches 626 and 624 are closed (turned ON) to allow the Vsetvoltage to be reset as the measured voltage Vmea, such that the biasgenerator reference voltage is Vset (i.e. equal to Vmea) plus Vcc. Atthe end of the heating ON cycle the transistor switches 434 and 624 arere-opened and transistor switch 622 is closed to restart the heating OFFcycle. This process is repeated until the heated tube reaches thepredetermined temperature and then transistor switch 420 will open toprevent further heating ON cycles from occurring until the temperaturefalls below the predetermined temperature. It is noted that the trackand hold sampling period (T) may be activated multiple times during aheating ON cycle or only activated after multiple heating on cycles,such as after 2, 5, 10, 15 or more heating ON cycles rather than forevery heating ON cycle or in other such arrangements. Furthermore thetrack and hold circuit 640 sampling period (T) may be activated once ormultiple times during a therapy session.

Advantageously providing an actual measure of the voltage at the wirejunction 507 between the two heating wires 506, 508 allows for the biasgenerator to provide a more accurate reference voltage to the sensingcircuit 428. The voltage drop on heating wire 506 or heating wire 508relative to each other may vary due to different factors such asdeteriorating resistance of connectors for example due to dirt in theconnectors or differences in wire gauge thicknesses due to manufacturingtolerances. Measuring the actual voltage at the wire junction 507between the two heating wires 506, 508 will allow for adjustment in thevoltage due to these variations. Furthermore measuring the voltage atthe wire junction 507 between the two heating wires 506, 508 may allowthe use of heating wires having different resistance levels. Thus thebias generator 618 is independent of the resistance of the heatingwires.

A further example of a system using measured voltage for the biasgenerator voltage source is shown in FIG. 20C. In this arrangement thereis no requirement for a transistor switch 622 to switch OFF the Vccvoltage source 614 as the track and hold circuit sets the bias measuredvoltage 616 to be equal to the voltage in the heating circuit for boththe heating ON and heating OFF cycles. The Vcc bias source voltage 614is linked to the set measured voltage (Vset) 616 such that the Vcc biassource voltage is provided plus the set measured voltage (Vset) 616 tothe sensing resistor 426 of the sensing circuit 428. It is the setmeasured voltage (Vset) 616 that is adjusted depending upon whether theheating circuit is ON or OFF. The transistor switch 628 is closed for asampling period to allow the voltage through the sensing circuit to bemeasured by the capacitor 630 at the commencement of the heating ON andheating OFF cycles. After the sampling period the transistor switch 628is opened so that the stored measured voltage can be read from thecapacitor 630 and Vmea is provided to the bias generator voltage set(Vset) 616 to set the bias generator voltage source. By sampling at boththe commencement of heating ON and heating OFF cycles the Vset valuewill be adjusted to equal the voltage in the heating circuit which willvary between a voltage level dependent on the voltage at the wirejunction 507 between the two heating wires 506, 508 or 0 volts when theheating circuit is OFF.

FIG. 35 shows an example of how the transistors switches 434, 624, 626and 628 may function in the system shown in FIG. 20C. For the heatingOFF cycle transistor switches 434 and 628 are open or OFF and switches624 and 626 are closed or ON resulting in no voltage supply beingprovided to the heating circuit 402 and the track and hold circuit is inthe hold state. The switch 624 is closed to allow the bias sourcevoltage Vcc plus Vset (in this situation 0 volts) to be provided to thesensing circuit 428 and switch 626 is closed so the sensed voltage maybe provided to the temperature control block 432. At the end of theheating OFF cycle the system switches to an ON sampling perioddesignated T_(on) and switch 628 is closed or turned ON together withswitch 434 to provide voltage from the voltage supply to the heatingcircuit to commence heating. Simultaneously switches 624 and 626 areturned OFF during the sampling period T_(on) to provide an unbiasedcircuit for the capacitor 630 to track the voltage in the heatingcircuit and optionally providing the held voltage from capacitor 627 tothe temperature control block and over temperature cut out circuit. Atthe end of the sampling period switch 628 is opened or turned OFF andswitches 624 and 626 closed or turned ON to allow monitoring of thesensed temperature. The capacitor 630 provides the measured voltage fromthe heating circuit Vmea to the bias generator Vset 616 such that thebias voltage remains constant over the amplifier 430 as the bias sourcevoltage Vcc. At the end of the heating ON cycle and at the commencementof the heating OFF cycle a second sampling period T_(OFF) is performedby opening or turning OFF switches 434, 624 and 626 and closing orturning ON switch 628. The voltage in the heating circuit is againtracked by the capacitor 630 but as no voltage is supplied to theheating circuit the value should be zero. At the end of the samplingperiod T_(OFF), the switch 628 is opened or turned OFF and the switches624 and 626 are closed or turned ON to allow monitoring of the sensedtemperature to recommence. This cycle may be repeated during the use ofthe heated tube. Alternatively the sampling periods T_(ON) and T_(OFF)may be performed once and recorded by a microprocessor that thenprovides the correct Vset value for the heating ON and heating OFFcycles. The measured voltage from each sampling period, T_(ON) andT_(OFF), may also be performed multiple times during a therapy sessionand the value recorded or stored for use during the heating ON and OFFcycles respectively.

It is also noted that transistor switch 626 and capacitor 627 areoptional components in the circuit.

In a further alternative bias generator arrangement as part of a heatedtube control system is shown in FIG. 20D. In this arrangement a biascurrent source is provided rather than a bias voltage source. The biascurrent source may include for example a current mirror circuit such asa Wilson current mirror circuit. In this arrangement two additionalresistors of equal resistance 658 and 660 are provided to balance thevoltage across the sensing circuit 428 irrespective of whether theheating circuit is ON or OFF. The two additional resistors 658 and 660are provided to the opposite side the sensing circuit 428 with a circuitwire taken from a position 662 between these resistors to ensure thevoltage provided when the transistor switch 434 is closed isapproximately half the voltage supply 440 and approximately equals or issimilar to the voltage provided to the temperature sensor 410. Theadditional wiring comprising resistors 650 and 652 may be locatedanywhere in the system and would preferably be located close to thepower supply source. A current source 642 is provided to ensure acurrent runs through the temperature sensor 410 and a voltage dropthrough the temperature sensor 410 can be recorded. The system functionsin the following manner:

When switches 420 and 434 are closed a voltage is supplied to both theheating resistance wires 506, 508 in the heating circuit 402, that eachcomprise resistors as shown in FIG. 18, and through the wires comprisingresistors 650 and 652. Thus providing a Vsupply/2 voltage source on theleft side of the sensing circuit to compare to the Vsupply/2 plustemperature sensor 410 voltage on the right hand side of the sensingcircuit. The difference in voltage is the voltage of the temperaturesensor 410 and is used to determine the temperature of the heatingcircuit.

When switch 420 is open no voltage is supplied to the heating circuit402 or through the wire comprising resistors 650 and 652. Thus the lefthand side of the sensing circuit is provided with 0 volts. The currentsource 642 provides a current through the temperature sensor 410 toallow the voltage across the temperature sensor 410 to be measured andto be provided to the right hand side of the sensing circuit to becompared to the 0 volts. Thus the presence of the current source 642allows for a voltage, that varies only as a function of the temperatureof the temperature sensor 410 and not the ON/OFF state of the heatingcircuit 402, to be provided to the amplifier 430 of the sensing circuitto determine a voltage for determining the temperature of thetemperature sensor 410.

Another alternative bias generator arrangement as part of a heated tubecontrol system is shown in FIG. 20E. In this arrangement resistors 603and 605 have been introduced with a resistance value relationship beingthat 603 is three times that of 605 (603=3×605). This produces a voltagevalue at the wire junction between 603 and 605 of approximately half ofthat found in the wire junction 507 between the two heated wires 506,508, or approximately a quarter of the supply voltage (Vsupply) 440.

In this configuration, the voltage difference between the wire junctionbetween 603 and 605 and the wire junction 507 between the two heatedwires 506, 508 is a quarter of the supply voltage (Vsupply) 440.Depending on whether the heating circuit is switched ON or OFF, thisvoltage difference across the sensing resistor 426 will be ofapproximately the same amplitude however in the opposite direction orsense. This allows the magnitude of the voltage across the temperaturesensor 410 to be substantially the same irrespective of whether theheating circuit is switched ON or OFF by the transistor switches 420,434, the only difference being that the sense of the voltage wouldswitch from positive or negative depending on the state of thetransistor switches 420, 434. Accordingly, magnitude of the voltageacross the sensing resistor 426 will be the same irrespective of whetherthe heating circuit is switched on or off.

Thus the sensing circuit 428 includes a sensing resistor configured toprovide an output to indicate the temperature of a sensor positioned inthe heated conduit and a bias generator circuit configured to provide areference voltage to the sensing resistor to allow determination of thetemperature of the heated conduit as a function of a voltage drop acrossthe sensing resistor during both heating ON and heating OFF cycles,wherein a direction of the voltage drop across the sensing resistorchanges when the heating circuit is ON compared to when the heatingcircuit is OFF.

A full wave rectifier circuit 629 may also be introduced in thisembodiment downstream of the amplifier 430. The rectifier retains theamplitude of the output from the amplifier 430 and conditionallytransforms the polarity of the output so that it is uniformly positiveirrespective of whether the voltage output from the amplifier 430 ispositive or negative. It should be understood that the full waverectifier circuit 629 may produce a uniformly negative output ifdesired.

As a result, the output from the amplifier 430 which is thenconditionally transformed by the full wave rectifier 629 is proportionalonly to the temperature sensor 410 irrespective of whether the heatingcircuit is switched ON or OFF, and can be used to as an input to thecomparator 436 or the temperature control block 432.

It is to be understood that any one of the above alternative biasgenerator arrangements may also be used as part of the circuitconfigurations shown in any one of the circuits shown in FIG. 21, 22 or27 or other control circuit configurations would be understood by aperson skilled in the art.

Additional Temperature Measuring Circuit Arrangement

FIG. 36 illustrates an additional circuit arrangement 1000 to allowmeasurement of the temperature of a 3 wire heated tube whether the tubeis being heated or not. This system may use a capacitor 1002 and maymeasure either the rate of discharging of the capacitor 1002 or the rateof charging of the capacitor 1002.

As illustrated in FIG. 36, the voltage at a junction 1004 may be known(Vsupply, or 24V), and the impedance (or resistance) of a circuit loop1006 may be a constant value, save for a resistance of a thermistor1008. The resistance of the thermistor 1008 may be a function of itstemperature. Therefore the rate of charge and/or discharge at thecapacitor 1002 may be proportional to the resistance of the thermistor1008. In addition, the rate of discharging/charging (e.g. as shown inFIG. 37) may provide an indication of the resistance of the thermistor1008 which may be used to determine a temperature of the heated tube.The slope and/or shape of the curve (which may be the basis fordetermining the temperature of the heated tube) may change depending onthe resistance of the thermistor 1008.

The capacitor 1002 may be located in series with the thermistor 1008 forthe heated tube. In addition, the thermistor 1008 may be located betweenthe two heating wires 1010 and 1012. Each of heating wires 1010 and 1012may include or act as a resistor. The capacitor 1002 may be alsoconnected in parallel between a junction 1014 between two resistors 1016and 1018 and a junction 1020 between the two heating wires 1010 and 1012such that the voltage on each side of the capacitor 1002 is known. Forexample, a resistance value of the heating wire 1010 may be equal to theresistance value of the resistor 1016 and the resistance value of theheating wire 1012 may be equal to the resistance value of the resistor1018, so the voltage on each side of the capacitor 1002 may be zero. Thecapacitor 1002 may discharge when the two switches 1022 and 1024 on eachside of the capacitor 1002 are closed, and the rate of dischargedetermined. Preferably, the switches 1022 and 1024 are opened/closed asa set, and operated with respect to the switch 1026 to control chargingand/or discharging sequence across the PWM load cycle.

The rate of total discharge from a complete charge may be measured inone form, and in another, the instantaneous rate of discharge as well asthe voltage of the capacitor 1002 may be used to determine thethermistor resistance/temperature. Preferably, the capacitor 1002 willbe connected to the circuit loop 1006 only during a ‘stable’ period of aPWM load cycle, and not during a switching period. Specificdischarging/charging shapes of capacitors may be chosen, such asdual-slope or quad-slope. In another form, an integral of the voltageacross the capacitor 1002 across the PWM cycle (or area under the curvein FIG. 37) may be obtained to determine the thermistor value.

The capacitor 1002 may be charged by another power supply, such as abattery (not shown) or by the 24V power supply via another circuit andswitch (Not shown). The capacitor 1002 may be used to measure the rateof voltage decay or storage during a steady state of the heating ornon-heating phases of the PWM. In some arrangements the rate may only bemeasured during either the ON or the OFF phase of the heating cycle ormay be measured during both phases. The circuit may be configured tocarry out temperature measurements at predetermined periods, such as forexample every Nth heating ON or heating OFF cycles. In somearrangements, an amplifier 1028 may be used to provide an amplifiedsignal indicating the voltage across the capacitor 1002.

One example of a suitable capacitor may be a NP0 capacitor with a smallcapacity such as 1 nF (Nano Farads). This may allow for the charge inthe capacitor to have only a small impact on the thermistor duringdischarge, and low self-heating characteristics.

The capacitor 1002 may have a discharge period that is short to occurwithin a single heating ON or heating OFF cycle. Alternatively thecapacitor 1002 may have a long discharge time that occurs over multipleheating ON and heating OFF cycles. A capacitor with a long dischargetime may also cancel out any temporary short-term fluctuations or errorsin measurement which may be advantageous. If a long discharge timecapacitor is used then the residual voltage in the capacitor 1002 uponfull discharge may provide an indication of the voltage error in theheating circuit.

The thermistor resistance may be pre-calibrated or self-calibrated basedon comparing a resistance of the thermistor 1008 at a known temperaturebased on a sensed temperature measured from a sensor (not shown). Forexample if the system includes an ambient temperature sensor then thetemperature measured by this ambient temperature may be used tocalibrate the resistance measurements received from the thermistor 1008.Such a measurement may be performed upon start-up of the system.

Heated Tube Control—Temperature Sensing with Tube Type Detection andActive Over Temperature Protection

Referring to FIG. 21, a sensing and control circuit configuration 450according to another sample embodiment allows for discrimination betweendifferent values of the temperature sensor (e.g. thermistor value as anindicator of tubing type) to permit changes in system performance tocompensate for changes in the characteristics of the tube types (e.g.pressure drop versus bore/internal diameter). For each tube type usedwithin the system there should not be an overlap in the resistancesobtained from using the different thermistors within the specifiedoperating temperature range of the heated tube, for example between 0°C. and 45° C., preferably between −5° C. and 50° C. For example, a 15 mminternal diameter heated tube may include a temperature sensor with athermistor value of 10 kΩ and a 19 mm internal diameter heated tube mayinclude a temperature sensor with a thermistor value of 100 kΩ. FIG. 23shows the characteristic curves for each of these example thermistorvalues. This allows the thermistor resistance value (or sensed voltage)to be used to detect the type of heated tube being used in the system.Thus, any compensation for air path performance can be adjustedautomatically (without user intervention) for each tube type, ifrequired. It should be appreciated that more than two types of tubes maybe detected in the system by using multiple comparator and gains.Detection of the tube type can also be used to adjust the amplifier gainand increase the amplitude of the temperature sense signal for a lowersensitivity (higher value NTC thermistor) circuit.

The signal gain may be adjusted so that the same over temperaturethreshold/circuit is used for different tube types (e.g. differentinternal diameters).

The circuit configuration 450 of FIG. 21 includes all the componentsshown in the circuit configuration 400 shown in FIG. 20 and the samenumbers are used to identify the similar components. The circuitconfiguration 450 comprises an additional tube type detect circuitcomprising a comparator 452 to compare the sensed voltage from amplifier430 with a voltage reference V_(ref2) that identifies a specific heatedtube resistance value to identify if a first tube type (e.g. size) isattached to the system. If sensed voltage is equal to and/or greaterthan the voltage reference V_(ref2) then the first tube type isdetermined as attached to the system and a gain is added via amplifier454 to the sensed voltage so that the same voltage value is applied tothe comparator 436 for the over-temperature control circuit. If thesensed voltage from amplifier 430 is not equal to and/or lower than thevoltage reference V_(ref2) a second tube type is determined as attachedto the system and no gain is added to the sensed voltage. In this mannerthe same threshold voltage for the over temperature detection is usedfor both heated tube types. It should be appreciated that more than twotypes of tubes may be detected in the system by using multiplecomparators and gains.

In an alternative embodiment the system may detect the differentresistances of the different tube types in a similar manner but insteadof adding a gain using amplifier 454 the comparator may use differentreference voltages V_(ref) for each of the different tube types.

Heated Tube Control—Temperature Sensing with Tube Type Detection, ActiveOver Temperature Protection, and Connect Fault Detection

Extreme variations in the temperature sense signal can also be used todetect electromechanical faults in the tubing circuit or in theelectrical connection of the tubing to the system. This is achieved withthe window comparator shown in FIG. 22 which may comprise resistors R2,R3, R4 which are biased by a voltage, e.g. 5V. This provides a morereliable connect fault detection than current heated tube systems on themarket that use over-current and current spark detection of fault sites.

The sensing and control circuit configuration 500 shown in FIG. 22includes all the features shown in the circuit configuration 450 of FIG.21 with like components identified with the same number. The circuitconfiguration 500 includes a tube fault detection circuit comprisingthree resistors 560, 562 and 564, that are used to set the windowthreshold of sensed voltages expected from a correctly working system. Asource voltage 566, that is the same as that used in the bias generator418, and a ground 568 are used to set the window thresholds of thesensed voltages. The comparators 570 and 572 compare the voltagereceived from the amplifier 430 with the window thresholds and if thesensed voltage is outside the expected range then a tube fault isdetected and a signal is sent to the temperature control block 432 toopen the transistor switch 434 to prevent power to the system.

The tube fault detection system is also able to detect the correctconnection of the heated tube to the system. The control system hasthree connectors attached to the ends of wires 404, 406 and 408 that areadapted for connection with connectors on the ends of the three wires504, 506 and 508 of the heated tube circuit 402. The connectors arearranged such that the last connectors to connect are those relating tothe sensing wire 504. This ensures that if the heated tube is notcorrectly connected a fault will be detected in the control system asthe voltage sensed by sensing resistor 426 will be 0V. This faultdetection system will detect faults such as short circuits, opencircuits, wiring faults or connection faults.

It should be appreciated that in the three sample embodiments of theheated tube control circuits discussed above, the circuit may beconfigured to disable heating in the event of a fault in the temperaturesensor that renders it open or short circuited. This feature may beprovided as an additional safety measure, for example in the embodimentsin which the circuit comprises includes the thermal fuse or in theembodiments in which the thermistor is provided to a fixture within thecuff.

Heating Plate Control—Overheating Prevention

The PAP system may operate according to various control algorithms, forexample as disclosed in U.S. Patent Application Publication 2009/0223514A1. The ambient humidity sensor (e.g., the temperature sensor) providedin the humidifier may be close to the heating plate of the humidifierand the operation of the ambient humidity sensor(s) may be affected bythe heating plate. For example, the heating plate temperature sensor maybe an NTC sensor that experiences “drift,” i.e., the resistance of theNTC sensor rises above the specification for the NTC sensor. The driftcauses the NTC sensor to detect a temperature lower than the actualtemperature of the humidifier heating plate. In order to prevent theheating plate from being heated to an unsafe temperature, it is possibleto provide a control algorithm that is designed to prevent heating ofthe heating plate when the temperature measured by the heating platetemperature sensor and the temperature measured by the humidity sensor,when considered together, are regarded as implausible.

Referring to FIG. 24, a control algorithm may be provided to preventoverheating of the humidifier heating plate. The control algorithm maybe run concurrently with any of the PAP system control algorithmsdisclosed in U.S. Patent Application Publication 2009/0223514 A1. Thecontrol algorithm starts in S100 and proceeds to S110. In S110 it isdetermined if the heating plate temperature T_(HP) is lower than a firstpredetermined heating plate temperature T_(HP1) and whether the sensedtemperature T_(SEN) detected by the humidity sensor is higher than aminimum sensed temperature T_(SENMIN). The first predetermined heatingplate temperature T_(HP1) may be the minimum temperature of thehumidifier heating plate that is plausible. For example, very cold watermay be placed in the humidifier, but ice should not be. So a firstpredetermined heating plate temperature T_(HP1) may be, for example,between about 0° C. and 4° C., such as about 2° C. The minimum sensedtemperature T_(SENMIN) may be a minimum ambient temperature at which thePAP system is recommended to be used. For example, the minimum sensedtemperature _(SENMIN) may be between about 3° C. and 8°, such as about5° C.

If the temperature of the heating plate T_(HP) is lower than the firstpredetermined heating plate temperature T_(HP1) and the sensedtemperature T_(SEN) is higher than the minimum sensed temperatureT_(SENMIN) (S110: Yes), the control proceeds to S120 and prohibitsheating the humidifier heating plate. It is noted that the answer toboth queries in S110 must be YES to proceed to S120. If the answer toeither query is NO, then the process moves to S115, which is describedin detail below. An acknowledgeable error message ERROR MESSAGE 1 isdisplayed in S130. For example, the display 4 may display“HUMIDIFIER_THERMISTOR_OPEN.” The user or operator may acknowledge theerror message, for example by pressing one of the inputs 6 and/or thepush button dial 8. After the error message is displayed, the controlproceeds to S140 and it is determined whether the time t that the PAPsystem has been operating under the conditions checked in S110 is lessthan a first maximum time t_(MAX1). The first maximum time t_(MAX1) maybe, for example, 15 minutes. If the conditions checked in S110 haveoccurred for more than the first maximum time (S140: Yes), the controlproceeds to S145 and a second error message ERROR MESSAGE 2 is displayedon the display of the PAP system. The control then proceeds to S150 andoperation of the PAP system is stopped.

The second error message ERROR MESSAGE 2 may be“HUMIDIFIER_HW_OVERPROTECTION_FAILURE.” The second error message ERRORMESSAGE 2 can not be acknowledged by the user or operator. The seconderror message ERROR MESSAGE 2 may only be removed by the user oroperator by clearing the PAP system with a power cycle, i.e., by turningthe PAP system off and then back on.

If the conditions checked in S110 have not occurred for longer than thefirst maximum time (S140: No), the control returns to S110 to check theheating plate temperature T_(HP) and the sensed temperature T_(SEN).

If the heating plate temperature T_(HP) is higher than the firstpredetermined heating plate temperature T_(HP1) and/or the sensedtemperature T_(SEN) is lower than the minimum sensed temperatureT_(SENMIN) (S110: No), i.e. either or both of the queries output NO, thecontrol proceeds to S115 and determines whether the heating platetemperature T_(HP) is lower than a second predetermined heating platetemperature T_(HP2) and whether the sensed temperature T_(SEN) is higherthan a first maximum sensed temperature T_(SENMAX1). The first maximumsensed temperature T_(SENMAX1) and the second predetermined heatingplate temperature T_(HP2) may be temperatures that are anticipatedduring operation of the PAP system. For example, it may be anticipatedthat whenever the sensed temperature is above 40° C., then the heatingplate temperature will be above 25° C.

If the heating plate temperature T_(HP) is lower than the secondpredetermined heating plate temperature T_(HP2) and the sensedtemperature T_(SEN) is higher than the first maximum sensed temperatureT_(SENMAX1) (S115: Yes), the control proceeds to S135 and heating of thehumidifier heating plate is prohibited. It is noted that the output ofboth queries in S115 must be YES to proceed to S135. If the output ofeither query is NO, then the process moves to S125, which is describedin more detail below. The control then proceeds from S135 to S145 andthe second error message ERROR MESSAGE 2 is displayed. The control thenstops the PAP system in S150.

If the heating plate temperature T_(HP) is higher than the secondpredetermined heating plate temperature T_(HP2) and/or the sensedtemperature T_(SEN) is lower than the first maximum sensed temperatureT_(SENMAX1) (S115: No), i.e. either or both of the queries output NO,the control proceeds to S125 and it is determined if the sensedtemperature T_(SEN) is higher than a second maximum sensed temperatureT_(SENMAX2). The second maximum sensed temperature T_(SENMAX2) may behigher than the first maximum ambient temperature T_(SENMAX1) and may bean upper limit on the temperature detected by the humidity sensorregardless of the detected heating plate temperature. For example,T_(SENMAX2) may be between about 45° C. and 55° C., for example about50° C. as this temperature may clearly indicate that the humidifier isoverheated (e.g., irrespective of the heating plate temperature), andmay provide sufficient margin for normal operation even in 35° C.ambient. The second higher maximum sensed temperature T_(SENMAX2) is anadditional check to ensure that the humidity sensor is not too hot. Thischeck is done every time one of the queries in S115 outputs NO. It isnoted that if the sensed temperature is lower than the first maximumsensed temperature T_(SENMAX1) then the sensed temperature should alsobe below the second maximum sensed temperature T_(SENMAX2) if the secondmaximum sensed temperature T_(SENMAX2) is higher than the first maximumsensed temperature T_(SENMAX1). Thus this check is particularly usefulwhen the heating plate temperature T_(HP) is higher than the secondpredetermined heating plate temperature T_(HP2).

If the sensed temperature T_(SEN) is lower than the second maximumambient temperature (S125: No), the control returns to S100 and startsagain.

It should be appreciated that the first and second error messages may bethe same. For example, the display 4 of the PAP system may display“HUMIDIFIER FAULT” for both the first and second error messages.However, the first error message represents a recoverable system errorand is acknowledgeable by the user or operator and may be cleared,whereas the second error message represents a non-recoverable systemerror and can not be acknowledged and cleared by the user or operatorexcept through a power cycle (turning the PAP system off and then backon).

Heating Plate Configuration

Referring to FIG. 29, the humidifier heating plate 900 may comprise aplate 902 formed of a heat conducting material. The heat conductingplate 902 may be made of, for example, metal, such as a nickel chromealloy or anodized aluminum. A heating element 906 may be provided on theheat conducting plate 902. The heating element 906 may be formed from aresistive film, and may be formed by, for example, stamping or etching aresistive foil. An insulating layer 904 may cover the heating element906. For stamping, the resistive film 906 is inserted between twoinsulating films 904. For etching, the resistive film 906, with anattached insulating film 904 on one of its sides, is covered by a secondinsulating film 904. The insulating film 904 may be formed of, forexample, KAPTON®.

The heating plate 900 of the humidifier may further comprise athermistor 908. The thermistor 908 may also be formed from a resistivefilm. The thermistor may be cut, stamped, or etched from a suitableresistive foil, for example, a metal foil, similar to the heatingelement 906. A plurality of wires 910, 912, 914 may be attached to theheating element 906 and the thermistor 908. The wires 910, 912, 914 maybe connected to the heating element 906 and the thermistor 908 by, forexample, solder 916.

Referring to FIG. 30, a humidifier heating plate 900 according toanother sample embodiment may comprise a thermistor 909 that has azig-zag shape. The thermistor 909 may be integrally formed with theheating element 906 by forming the thermistor 909 and the heatingelement 906 from a suitable resistive film, e.g. a resistive metal foil.Two insulating films 904 insulate the top and bottom surfaces of theheating element 906 and the thermistor 909. The integrated thermistor909 may be excited by a constant current so the resistance changes withtemperature are converted into a voltage that can be amplified and usedby the humidifier heating control circuit.

Referring to FIG. 31, a humidifier heating plate 900 according toanother sample embodiment may comprise a heating element 906 formed of aresistive film formed of a first material and a thermistor 909 formed ofa resistive film of a second material different from the first material.The second material that forms the thermistor 909 may have a highresistance than the first material. The wires 910, 912, 914 may beultrasonically welded at points 918, 920, 922 to the heating element 906and the thermistor 909. The connection point 922 connects the wire 910to both the heating element 906 and the thermistor 909.

Referring to FIG. 32, a humidifier heating plate 900 according toanother sample embodiment comprises a heating element 906 covered by aninsulating layer 904. A thermistor 909 is provided separate from theheating element 906 and the insulating layer 904. It should beappreciated that the thermistor 909 may also be insulated by separateinsulating films. Wires 928, 930 connect the heating element 906 to thepower supply and humidifier heating control circuit and wires 924, 926connect the thermistor 909 to the power supply and humidifier heatingcontrol circuit.

Referring to FIG. 33, a humidifier heating plate 900 according to afurther sample embodiment includes a heating element 906 insulated bytwo insulating films 904. The heat conducting plate 902 includes a freearea 932 which may accommodate at least one electric circuit that may beused to perform temperature measurements without the use of athermistor. For example, if the heater element 906 is made of resistivefilm of a material whose resistance increases with temperature, theelectric circuit can measure the heater plate temperature by measuringthe resistance of the heating element.

The provision of an integrally formed heating element and thermistor, asshown for example in FIG. 30, overcomes a problem experienced withdiscrete thermistors that may tend to crack when used to measuretemperature in the humidifier heating plate. The provision of anintegrally formed heating element and thermistor also provides improvedresistance to mechanical shocks and provides more reliable humidifiertemperature control. Integrally forming the heating element and thethermistor also simplifies the assembly process as there is no need tosolder a discrete thermistor to the humidifier heating plate.

Heated Tube Control—Overheating Prevention

The NTC sensor in the heated tube may also experience drift. A drift inthe resistance of the temperature sensor in the heated tube may causethe temperature sensor to detect a temperature lower than the actualtemperature of the heated tube. This could lead the PAP system tooverheat the heated tube.

Referring to FIG. 25, a control algorithm may be provided to preventoverheating of the heated tube. The control algorithm may be runconcurrently with any of the PAP system control algorithms disclosed inU.S. Patent Application Publication 2009/0223514 A1 and with the heatingplate control algorithm of FIG. 24. The control starts in S200 andproceeds to S210. In S210 it is determined if the heated tubetemperature T_(HT) is lower than the minimum sensed temperatureT_(SENMIN). If the temperature of the heated tube T_(HT) is lower thanthe minimum ambient temperature T_(SENMIN) (S210: Yes), the controlproceeds to S220 and an acknowledgeable error message ERROR MESSAGE 3 isdisplayed in S230. For example, the display 4 may display“HEATED_TUBE_CURRENT-TRIP.” The user or operator may acknowledge theerror message, for example by pressing one of the inputs 6 and/or thepush button dial 8. After the error message is displayed, the controlproceeds to S240 and it is determined whether the time t that the PAPsystem has been operating under the conditions checked in S210 is lessthan the first maximum time t_(MAX1). If the conditions checked in S210have occurred for more than the first maximum time (S240: Yes), thecontrol proceeds to S245 and a fourth error message ERROR MESSAGE 4 isdisplayed on the display of the PAP system. The control then proceeds toS250 and operation of the PAP system is stopped.

The fourth error message ERROR MESSAGE 4 may be“HEATED_TUBE_HW_OVERPROTECTION_FAILURE.”. The fourth error message ERRORMESSAGE 4 can not be acknowledged by the user or operator. The fourtherror message ERROR MESSAGE 4 may only be removed by the user oroperator by clearing the PAP system with a power cycle.

If the conditions checked in S210 have not occurred for longer than thefirst maximum time (S240: No), the control returns to S210 to check theheated tube temperature T_(HT) against the minimum sensed temperatureT_(SENMIN).

If the heated tube temperature T_(HT) is higher than the minimum sensedtemperature T_(SENMIN) (S210: No), the control proceeds to S215 anddetermines whether the power supplied to the heated tube P_(HT) isgreater than or equal to a first predetermined heated tube powerP_(HT1), whether the detected temperature of the heated tube T_(HT) islower than a first predetermined heated tube temperature T_(HT1) andwhether an elapsed time t is less than a second maximum time t_(MAX2).If the power P_(HT) supplied to the heated tube is greater than or equalto the first predetermined heated tube power P_(HT1), the detectedtemperature T_(HT) of the heated tube is less than the firstpredetermined heated tube temperature T_(HT1), and the elapsed time isgreater than the second maximum time t_(MAX2) (S215: Yes), i.e. allthree queries must output YES in S215, the control proceeds to S225 andthe heated tube is prevented from heating. The control then proceeds toS245 and the fourth error message ERROR MESSAGE 4 is displayed. Thecontrol then stops operation of the PAP system in S250.

If the power P_(HT) supplied to the heated tube is less than the firstpredetermined heated tube power P_(HT1), the detected temperature T_(HT)of the heated tube is greater than the first predetermined heated tubetemperature T_(HT1), and/or the elapsed time is less than the secondmaximum time t_(MAX2) (S215: No), i.e. one or more of the three queriesin S215 outputs NO, the control returns to S200 and starts over.

It should be appreciated that the third and fourth error messages may bethe same. For example, the display 4 of the PAP system may display “TUBEFAULT” for both the third and fourth error messages. However, the thirderror message represents a recoverable system error and isacknowledgeable by the user or operator and may be cleared, whereas thefourth error message represents a non-recoverable system error and cannot be acknowledged and cleared by the user or operator except through apower cycle (turning the PAP system off and then back on). It shouldalso be appreciated that the third and fourth error messages may be thesame as the first and second error messages, e.g. “HUMIDIFIER FAULT.”

As noted with respect to FIG. 23, a 15 mm internal diameter heated tubemay include a temperature sensor with a thermistor value of 10 kΩ and a19 mm internal diameter heated tube may include a temperature sensorwith a thermistor value of 100 kΩ. The PAP system may be operated over arecommended temperature range. For example, the lowest recommendedsensed (ambient) temperature at which the PAP system may be operated is5° C., and the highest recommended sensed temperature at which the PAPsystem may be operated is 35° C. If the system is stored at the lowestrecommended ambient temperature, e.g. 5° C., it is expected that thesystem will warm to above the lowest recommended ambient temperature inabout 15 minutes. Over the recommended temperature range, the resistancevalues of the NTC temperature sensor in the heated tube will vary. Forexample, the temperature sensor in a 15 mm internal diameter heated tubemay have a resistance ranging from about 8 kΩ to 28 kΩ, and thetemperature sensor in a 19 mm inner diameter heated tube may have aresistance ranging from about 80 kΩ to 750 kΩ. These ranges can bereduced by the heated tube control shown in FIG. 25, in particular bythe steps S210, S220, S230, S240, S245 and S250. If the temperature ofthe heated tube is below the lowest recommended sensed (ambient)temperature (i.e. T_(SENMIN)) for operation of the PAP system, thecontrol prevents heating of the heated tube. If this condition persistsfor more than 15 minutes (i.e. t_(MAX1)), the control stops the PAPsystem and displays an unrecoverable error message (i.e. ERROR MESSAGE4). Control of the heated tube in this manner reduces the resistancerange at which the PAP system can heat the heated tube. For example, the15 mm inner diameter heated tube may be heated across a resistance rangeof about 8 kΩ to 23 kΩ and the 19 mm inner diameter heated tube may beheated across a resistance range of about 80 kΩ to 250 kΩ.

Thermistor failures may be categorized by: (i) those that respondproportionally (negatively) to temperature, such as an NTC; (ii) thosethat carry a fixed resistance in series with the NTC element; and (iii)those that respond positively to temperature, i.e. increasing resistanceas the temperature rises. Of course, this is a spectrum for which theremay be mixed behaviour.

A 25° C. temperature rise is needed to change the resistance of astandard NTC from 23 kΩ to 8 kΩ or from 250 kΩ to 80 kΩ. Therefore anNTC at the extreme of 23 kΩ or 250 kΩ at 30° C. might need a 25° C.temperature rise to get to 8 kΩ or 80 kΩ respectively. A 25° C. rise on30° C. is 55° C., at which temperature the tubing has not reached itssoftening temperature.

A thermistor with a fixed offset pushing its resistance outside theoperating ranges will cause the PAP system to not heat the heated tube.A more subtle case where the resistance is within the operating range ismore difficult to detect. If the resistance rises with temperature, thePAP system will interpret this as cooling. As in the case with a fixedoffset, the resistance of the thermistor will either be pushed outsidethe operating range for heating, or it will be the subtle case that ismore difficult to detect.

To detect the subtle cases, a condition that occurs when the heated tubetemperature is unresponsive to significant applied power may beobserved. The PAP system may be designed to distribute power between theheating plate of the humidifier and the heated tube. For example, theheated tube may have priority over, for example, 60% of the availablepower. In the embodiments described in FIGS. 20-22, 36 W are availableto the heated tube. The criteria for the decision in S215 of the controlalgorithm of FIG. 25 may be set based on tests conducted at the extremesof the recommended ambient temperature operating range of the PAPsystem. At the minimum recommended sensed (ambient) operatingtemperature of 5° C. and supplying full power to the heated tube, thetemperature of the heated tube rose above 15° C. within 3 minutes. A 15°C. temperature increase corresponds to 15 kΩ for a 15 mm tube and 150 kΩfor a 19 mm tube. Therefore, if the temperature of the heated tube hasnot risen above 15° C. (i.e. Tim) after 3 minutes (i.e. t_(MAX2)) of 36W (i.e. P_(HT1)), the control can stop heating the heated tube beforethe heated tube is in danger of being damaged. It should be appreciatedthat other times and corresponding temperature measures may be used.

Heated Tube—Electro-Pneumatic Connection

The tube electrical connection may be made via a bayonet style connectorthat operates on an axis co-aligned with the tube pneumatic fitting, forexample as described herein in relation to FIGS. 8-17. The threecontacts may engage sequentially as shown in FIG. 22 with the sensorcontact remaining disconnected until full engagement of the connector ismade. The heating circuits are inactive until the tube presence isestablished. The signals may be arranged such that the temperaturesensor line is engaged last of the three conductors. The circuit doesnot recognise that a tube is connected until this line is connected. Theground line is the first line engaged and therefore the most accessibleconductor. It is also the line least likely to affect the operation ofthe circuit if it is inadvertently touched by the user.

Although the tube size (e.g. internal diameter) has been disclosed asbeing detected automatically upon connection, it should be appreciatedthat it is also possible that the tube size may be selected manually bythe user through the user interface of the humidifier and/or the flowgenerator.

The heated tube electrical circuit allows lower profile tubing and cuffmouldings. A single assembly operation completes both the pneumatic andelectrical connections between the tubing and the humidifier outletwhich makes treatment/therapy easier to administer. Automatic adjustmentof system performance with different tube types reduces, or eliminates,the need for clinician/patient adjustment of system settings.

The simpler tubing configuration is less expensive to manufacture. Usingactive over temperature detection reduces the cost of the tubingassembly and parts by eliminating the mechanical thermal cut-out switch.A three wire tubing circuit provides output end temperature sensingusing the heating circuit as part of the sensing circuit. Thus, theoverall tubing circuit has fewer connections and components and issimpler and less expensive to manufacture. The simpler tubing circuit iseasier to manufacture and makes automation more easily achievable.

The simpler tubing configuration allows for higher volume production.The electronic circuit uses standard components readily available forhigh production volumes.

It should be appreciated that the heated tube may optionally include athermal cut-out fuse/switch, for example if a stand-alone heated tubewith a separate power supply is used. Such a thermal cut-out fuse/switchis disclosed in, for example, U.S. Patent Application Publication2008/0105257 A1. It should also be appreciated that such a thermalcut-out/fuse, and/or other circuit configurations disclosed herein, maybe provided on a printed circuit board provided in the cuff of theheated tube.

Power Supply for Patient Interface

Referring to FIG. 26, a sample embodiment of a PAP system 600 comprisesa PAP device 602 connected to a patient interface 606. The PAP device602 may be a flow generator or a flow generator connected to ahumidifier. The PAP device 602 may be connected to the patient interface606 via a conduit 604 (e.g. a heated tube as described herein). Theconduit 604 provides for the transfer of power (e.g., electrical energy)from the PAP device 602 to the patient interface 606. Additionally,conduit 604 may be utilized to transfer data between the PAP device 602and the patient interface 606. The data transferred from the patientinterface 606 to the PAP device 602 may include, for example,information on various aspects of the patient interface, commands to thepatient interface, or a combination thereof.

As discussed above, the patient interface 606 may include varioussensors. The sensors may include, for example, a temperature sensor, ahumidity sensor, a flow and pressure sensor, a microphone (e.g. voice),a noise cancellation sensor, a G force sensor (to allow thedetermination of whether a patient wearing the patient interface islaying face down, sitting up, etc), motion sensing for alternative (toflow) breath detection, a gagging detection sensor, a pulse oximeter, aparticulates detector sensor, etc. In addition to the sensingfunctionality provided by the sensors, the sensors may also employvarious techniques for alerting a user. For example, a sensor mayinclude an LED that changes colour based on the particular property thatis being sensed. Alternatively, or in addition to, a sensor may includea speaker that may be used to alert a user based on a reading from asensor. Such speakers may also be used in conjunction with a microphoneto create an “anti-noise” signal to cancel out surrounding noise.

In addition to the sensors provided on the patient interface 606,various controllers may also be provided to the patient interface 606.Such controllers may include, for example, actuators that directlyhumidify the patient interface, an active vent, a speaker or alarm, anoise cancellation control, vibration control (e.g., to signal a patientto wakeup), lamps for light therapy, etc. It should also be appreciatedthat the patient interface may include manual switches, e.g. dials,and/or controls that the patient or clinician may operate to control thesystem.

The conduit 604 may use one wire to carry both data and power betweenthe PAP device 602 and the patient interface 606. Alternativeembodiments, however, may utilize multiple wires to carry data and/orpower between the PAP device 602 and the patient interface 606.

In further embodiments, the conduit that carries the power and databetween the PAP device and the patient interface may utilize anon-heated tube. In yet further embodiments, the transmission of dataover a link between the PAP device and the patient interface may befacilitated by utilizing CAN (Controller Area Network) or LIN (LocalInterconnect Network) buses. Such buses may be utilized to createalternative embodiments of circuits to read data from sensors andoperate controllers. In still further embodiments, an optical and/ortransformer isolation may be provided for the link.

A patient interface with sensors and/or controllers may provide a PAPdevice with an ability to control an active vent of the patientinterface. This may facilitate improved patient expiratory release. Thiscontrol may lead to reduced flow generator and blower sizes as thecorresponding vent flow is reduced. In turn this may create lower powerusage, longer battery life, smaller sized PAP devices, smaller sizedtubes (e.g., 10 mm), smaller sized patient interfaces, and may reducethe overall noise of the entire system and/or improve patient comfort.

Power Supply for Patient Interface System—Circuit for PAP Device

Referring to FIG. 27, a sample embodiment of a circuit 700 thatfacilitates the transfer of power and data from a PAP or humidifierdevice to a patient interface is shown.

The circuit 700 may include components of the sensing and controlcircuit 400 shown in FIG. 20. The same reference numbers are used toidentify similar components. In addition to those features found incircuit 400, circuit 700 may include a modem 708. The modem 708 mayprovide modulation and de-modulation functionality for data 704 that iscommunicated between the circuit 700 and an outside source. The outsidesource may include, for example, patient interface 50 as shown in FIG.15.

In addition to data 704, power 710 may also be provided. The power 710may be provided on the same signal line that carries the data 704.However, the power 710 may also be provided on a separate line that runsseparate from the data line.

Alternatively, or in addition, to the modem 708, a multiplexor may beprovided in order to combine multiple signals onto a single line. Thesensing wire 404 of the patient interface may be used to encode anddecode data for reading sensors and operating controllers by adding amultiplexing circuit to modulate data for the controllers of the patientinterface and demodulating signals from the sensor(s) of the patientinterface device. A multiplexor 431 may be provided to multiplex theoutput of the amplifier 430 so that false temperature control or overtemperature cut out does not occur. A multiplexor 433 may also beprovided to multiplex power onto the sensing wire 404. The multiplexormay also handle the de-multiplexing of an incoming signal into theoriginal respective signals. A multiplexor may also be added to circuitconfiguration 700 to multiplex incoming signals from data 704 and thetemperature reading from the NTC sensor 410.

Data 704 can include passive data. Such data, may include, for examplethe ambient air temperature within a patient interface or the amount ofpressure and flow in the patient interface. Data 704 may additionallyinclude commands. For example, the commands may include, an instructionthat a particular sensor is to take a measurement or turn off/on, thatan active vent on the patient interface is to be controlled, e.g.,opened and/or closed or proportionally opened and/or proportionallyclosed to actively control respiratory pressure and flows. Circuitconfiguration 700 may provide an encoding feature that encodes dataand/or commands before they are sent along the sensing wire 404.Similarly, data and/or commands received by circuit configuration 700may be decoded.

Circuit configuration 700 may also include functionality thatfacilitates the extraction of information from the received data. ThePAP device 602 may further take a given action based on the extractedinformation. For example, a sensor may transmit that the humidity in thepatient interface is above a certain threshold. Upon receiving thisdata, the PAP device, or humidifier, may take action to adjust thehumidity in the patient interface.

Power Supply for Patient Interface System—Circuit for Patient Interface

Referring to FIG. 28, a sample embodiment of a circuit associated with apatient interface that receives power and transfers data is shown.Circuit configuration 800 may be disposed at the patient interface endof tube 802, or may alternatively be disposed on the patient interface.In circuit configuration 800 both power 804 and data 806 are shown asbeing in communication with tube 802. In this sample embodiment, powerand data are utilizing one signal wire. However, as explained above,other embodiments may utilize wires that are dedicated to power and datarespectively.

Modem 808 provides modulation and demodulation functionality for data806. Power 804 may be provided to sensor 810 and/or controller 812.Likewise, the data 806 may be provided to sensor 810 and/or controller812. Thus, both the controllers and sensors can be linked up to thepower and data provided from an outside source (e.g., a PAP device).Further, like circuit configuration 700, circuit configuration 800 mayalso include multiplexors and/or encoders to facilitate the transfer ofdata and power. In alternative embodiments, a microprocessor may beadded to circuit configuration 800 to pre-condition signals, for exampleto compensate or calibrate raw sensor signals or to encode or compressdata. Additional embodiments may utilize an isolation circuit formedical safety where wires cannot be applied to the circuits. Forexample, a transformer, capacitor or optical coupling may be used toelectrically isolate the patient interface circuit for patient safety.

Sensor 810 may include, for example, sensors that detect temperature,humidity, flow and pressure, voice pattern or speech recognition,attitude detection (e.g., whether a patient is face down), breathingflow, gagging of the patient, oxygen saturation of the patient (e.g., apulse oximeter), or particulates (e.g., for safety).

Controller 812 may include controllers that accomplish various tasks,for example, actuators that directly humidify the patient interface, anactive vent, a speaker or alarm, a noise cancellation control, vibrationcontrol (e.g., to signal a patient to wakeup), etc.

The patient interface may also include light or optical sensing lamps.The patient interface may also be heated, e.g. a cushion or seal, toimprove patient comfort. The patient interface heating may be controlledvia the link. The patient interface may also include a controlledexpansion foam or membrane seal that may use a variable force controlledvia the link and patient interface circuit to improve the sealing of thepatient interface with the face of the patient. Foam and/or sealcharacteristics may also be sensed to provide a patient interface seal“fit quality” and transmit data to the PAP device via the link. Forexample, the compression of the cushion or seal may be sensed byelectrical resistance change and the data transmitted via the link tothe PAP device to determine fit quality and/or permit patient interfacecontrol adjustment and/or sealing force to improve fit by improvedcompliance to patient facial contours.

Although the invention has been herein shown and described in what isconceived to be the most practical and preferred embodiments, it isrecognized that departures can be made within the scope of theinvention, which is not to be limited to the details described hereinbut is to embrace any and all equivalent assemblies, devices andapparatus. For example, the heating wires may be PTC elements with avoltage regulation to limit the temperature of the wires and/or the airin the tube(s). As another example, one or more PTC or NTC wires may beused in conjunction with a resistor to limit the temperature of thewires and the air. As a further example, NTC wires may be used with acurrent regulator, or a measure resistance, to limit the temperature ofthe heating wires. The temperature sensing and heating may also beperformed using only two wires.

In this specification, the word “comprising” is to be understood in its“open” sense, that is, in the sense of “including”, and thus not limitedto its “closed” sense, that is the sense of “consisting only of”. Acorresponding meaning is to be attributed to the corresponding words“comprise,” “comprised” and “comprises” where they appear.

It will further be understood that any reference herein to known priorart does not, unless the contrary indication appears, constitute anadmission that such prior art is commonly known by those skilled in theart to which the invention relates.

What is claimed is:
 1. A sensing circuit for a heated conduit for use ina respiratory apparatus, the sensing circuit comprising: a sensing wirecoupled to a heating circuit for the heated conduit; a temperaturesensor coupled to the sensing wire and configured to measure thetemperature of the heated conduit; a sensing resistor coupled to thesensing wire and configured to provide an output to indicate thetemperature measured by the temperature sensor; and a bias generatorcircuit configured to provide a reference voltage to the sensingresistor to allow determination of the output as a function of a voltagedrop across the sensing resistor during both heating on and heating offcycles of the heating circuit, wherein the reference voltage isadjustable so that the reference voltage remains greater than a measuredvoltage across the sensing wire by a fixed value.
 2. The sensing circuitof claim 1, wherein the reference voltage is a sum of a fixed biassource voltage and a stored measurement voltage that corresponds to themost recent voltage measurement across sensing wire.
 3. The sensingcircuit according to claim 2, wherein the stored measurement voltagecorresponds to a voltage of the sensing wire measured during a heatingon cycle.
 4. The sensing circuit according to claim 2, wherein thestored measurement voltage corresponds to a voltage of the sensing wiremeasured during a heating off cycle.
 5. The sensing circuit of claim 1,wherein the bias generator circuit is configured to compare successivemeasurements of the voltage across the sensing wire and adjust thereference voltage based on a difference between the successivemeasurements.
 6. The sensing circuit of claim 1, wherein the biasgenerator circuit is configured so that the bias generator circuit doesnot provide the reference voltage to the sensing resistor while thevoltage across the sensing wire is being measured.
 7. The sensingcircuit according to claim 1, wherein when the heating circuit is on, abias source voltage is added to the measured voltage to provide thereference voltage.
 8. The sensing circuit according to claim 1, whereinwhen the heating circuit is off, the reference voltage is equal to abias source voltage.
 9. A control system for a heated conduit for use ina respiratory apparatus, the control system comprising: a power supplyto provide power to the heated conduit; a heating control circuitconfigured to control heating to obtain a predetermined temperature; andthe sensing circuit according to claim
 1. 10. A heated conduitcomprising the control system according to claim
 9. 11. A sensingcircuit for a heated conduit for use in a respiratory apparatus, thesensing circuit comprising: a sensing wire coupled to a heating circuitfor the heated conduit; a temperature sensor coupled to the sensing wireand configured to measure the temperature of the heated conduit; asensing resistor coupled to the sensing wire and configured to providean output to indicate the temperature measured by the temperaturesensor; and a bias generator circuit configured to provide a referencevoltage to the sensing resistor to allow determination of the output asa function of a voltage drop across the sensing resistor during bothheating on and heating off cycles of the heating circuit, wherein thereference voltage is generated from a bias source voltage and a voltageacross the sensing wire.
 12. The sensing circuit of claim 11 furthercomprising a capacitor and a capacitor switch between the bias generatorcircuit and the sensing wire.
 13. The sensing circuit according to claim12, wherein during a heating on cycle, the capacitor switch is in aclosed position so that the voltage across the sensing wire is stored inthe capacitor.
 14. The sensing circuit according to claim 13, whereinduring a heating off cycle, the capacitor switch is in an open positionso that the capacitor discharges the stored voltage to the biasgenerator circuit.
 15. The sensing circuit according to claim 14,wherein when the heating circuit is on, the bias source voltage is addedto the stored voltage to provide the reference voltage.
 16. The sensingcircuit of claim 12, wherein the bias generator circuit comprises a biasgenerator switch that allows the bias generator circuit to provide thereference voltage to the sensing resistor when the bias generator switchis in a closed position and prevents the bias generator circuit fromproviding the reference voltage to the sensing resistor when the biasgenerator switch is in an open position.
 17. The sensing circuit ofclaim 16, wherein the bias generator switch is in the closed positionwhen the capacitor switch is in an open position and the bias generatorswitch is in an open position when the capacitor switch is in a closedposition.
 18. The sensing circuit according to claim 11, wherein whenthe heating circuit is off, the reference voltage is equal to the biassource voltage.
 19. A control system for a heated conduit for use in arespiratory apparatus, the control system comprising: a power supply toprovide power to the heated conduit; a heating control circuitconfigured to control heating to obtain a predetermined temperature; andthe sensing circuit according to claim
 11. 20. A heated conduitcomprising the control system according to claim 19.